This invention is related to methods for producing brushware by injection molding, specifically methods of producing brushware by in-mold bristling techniques.
The variety of brands, designs, and styles of toothbrushes available in the United States today is truly staggering. Brushes are available in sizes and styles appropriate for babies, adults, dentures, sensitive gums, and other specialized needs. Brushes can be had in every color of the rainbow and decorated with logos ranging from mermaids and cartoon characters to trade names of various kinds. Most brushes are produced via a two part technique. The handles are produced by injection molding, and the bristles are later inserted into a head portion of the handle. One common technique for inserting the bristles into the brushes is to staple them. Bristles are folded around a metal staple which is pushed into pre-molded holes in the brush. The staple cuts its way into the brush handle, which holds it and the bristles securely. However, rough use can easily remove the bristles from the handle, leading to shedding, or, in a worst case scenario, release of the metal staple inside the mouth.
Techniques wherein the bristles are fused with the handles can be used to produce brushes where the bristles are much harder to remove from the brush. Either the bristles or the brush head, or both, are heated, and the bristles are inserted into holes in the handle, where they are retained by the cooling plastic. Exemplary techniques for brush production by fusion, such as those disclosed in U.S. Pat. Nos. 4,609,228 and 4,646,381, produce brushes with high bristle retention strength but retain the economic disadvantage that the brush is produced in a two-part process on two different machines. That is, the handles are still produced on a different machine than the one on which the bristles are inserted into the handle. It is thus desirable to produce a toothbrush using techniques which minimize the apparatus used, and consequently, the amount of time and number of personnel required to produce the brushes.
In-mold bristling processes, wherein the handle of the brush is injection molded around the bristles, have been used to produce a variety of different brushes. For example, U.S. Pat. No. 4,635,313 (the ""313 patent) to Fassler, describes an in-mold bristling process wherein the ends of the bristles are fused prior to the injection molding of the handle. The illustrative drawing on the front page of the patent shows a nail brush; however, the technique can also be used to produce toothbrushes. One concern in the production of brushes by this technique is the penetration (xe2x80x9cflashxe2x80x9d) of injection molded material through the bristle bundles into the face of the brush. This is not only unsightly but unhygienic because the excess material provides an excellent hiding place for bacteria and mold. To prevent this, the ""313 patent describes a method of sealing the opening of the injection mold through which the bristles enter the mold with a melted fuse at the end of the bristle bundles. U.S. Pat. No. 5,045,267 (the ""267 patent) to Weihrauch discloses a variation of the in-mold bristling technique described in the ""313 patent. However, in the ""267 patent, the fused ends of the bristle bundles are pulled against sleeves projecting from the end of the channels which lead into the mold. The tensile force holding the fuse against the sleeve further discourages injection molded material from penetrating the bristle bundles.
U.S. Pat. No. 5,143,424 to Boucherie also describes an in-mold bristling process. Bristles are loaded into one end of a two-ended magazine while, at the other end, the handle material is simultaneously injection molded into a previously loaded second end of the magazine. Each of the two ends of the magazine can hold the bristles for a single brush and mate with an injection mold to complete a mold cavity into which the handle is injection molded.
U.S. Pat. No. 5,823,633 to Weihrauch describes an in-mold bristling process similar to that described by the ""267 patent. However, in this invention, the fuseballs are not brought into sealing contact with the sleeve. Instead, they are maintained at a finite distance, between 0.1 mm and 2.0 mm, from the opening of the channel, allowing air to escape from the mold cavity through the channel. The gap increases the depth of the fuses within the handle, reinforcing the length of bristle bundle material immediately adjacent to the fuse and increasing the force required to remove the bristle bundles from the brush handle. However, this technique also allows injection molded material to penetrate the bristle bundle and flash over the head of the brush.
U.S. Pat. Nos. 5,458,400 to Meyer and 5,474,366 to Strxc3xctt, et al., describe techniques wherein a first section of the brush, including a portion of the head and at least part of the handle is injection molded before the bristles are inserted into the mold. The bristle bundles are inserted into holes in the first brush section, after which the rest of the brush is injection molded.
U.S. Pat. No. 5,609,890 to Boucherie describes an in-mold bristling process wherein the handle comprises two materials instead of a single injection molded material. The invention utilizes a molding machine which comprises at least two injection molding stations and a tuft feeding station. At the feeding station, the bristles are fed into a magazine, following which the ends of the bristles are fused. The magazine, which includes part of a mold cavity, is mated with the rest of an injection mold, completing the mold cavity. The first section of the brush, including the head, is injection molded, following which the magazine, still carrying the first injection molded section of the brush, is transferred to a second injection mold, whereat the remainder of the brush is injection molded.
In one aspect, the invention is a method for manufacturing brushes. The method includes the steps of inserting a plurality of bristle bundles into a first mold cavity in a magazine, manipulating at least one end of the bristle bundles, mating the first mold cavity portion with a second injection mold cavity portion in an injection mold, and injection molding at least a portion of a brush handle. The first and second cavity portions define the shape of the portion of the brush handle. The bristles may be inserted into the magazine from an endless supply or a supply of pre-cut bristles.
Manipulating may comprise adjusting the relative heights of the bristle bundles with respect to one another before the first part of the brush handle is injection molded. Within the individual bristle bundles, the relative heights of a portion of the bristles may also be adjusted with respect to each other at this time. A non-use side of the bristle bundles may be trimmed to produce a level plane, and a portion of the bristle bundle may be end-rounded before or following the step of injection molding. Following the initial adjusting step, the relative height of the bristle bundles with respect to one another may be inverted in a further adjusting step. Alternatively, manipulating may include fusing a non-use end of each bristle bundle to form a region having a greater diameter than that of the remainder of the bristle bundle. The fusion may be accomplished thermally or chemically and may be followed by pressing the fused ends against a portion of the first mold cavity portion. Thermal fusion may be accomplished by a contact heater, a non-contact heater, or hot air. If the bristles are fused thermally, they may be partially flattened while the fused ends are still warm. A portion of the brush handle may comprise polypropylene, cellulose propionate acetate, polyethylene terephthalate, or a thermoplastic polymer.
The process may further comprise removing the completed portion of the brush handle from the second mold cavity portion, mating the magazine and the portion of the brush handle with a subsequent mold cavity portion, and injection molding an additional portion of the brush handle. The completed portion of the brush handle and the subsequent mold cavity portion define the shape of the additional portion of the brush handle. The additional portion may comprise a thermoplastic elastomer, polypropylene, cellulose propionate acetate, polyethylene terephthalate, or a thermoplastic polymer. The completed portion of the brush handle may be at least partially supported by the bristle bundles when it is carried by the magazine to the subsequent mold cavity portion, but not all the bristle bundles need be retained in the completed portion of the brush.
The magazine may be arranged and constructed to hold bristle bundles corresponding to a plurality of brushes such that the plurality of brushes can be produced simultaneously. For example, the magazine may be arranged and constructed to hold bristle bundles corresponding to four brushes simultaneously. All of the brushes need not be the same color. The process may further comprise packaging, ornamenting, or labeling the completed brush. Ornamenting may include hot-stamping, stamping a decoration, or applying a label. An insert may be placed into the magazine to be incorporated into the completed brush. The insert may be a metal shank or a plastic insert.
In another aspect, the invention is a magazine for conveying bristle bundles along a brush making apparatus. The magazine includes a mold face, a mold cavity portion disposed in the mold face having the shape of part of a head of the brush, a back side, a clamping plate disposed between the mold face and the back side, and a plurality of channels extending through the magazine into the mold cavity for holding bristle bundles in a configuration corresponding to the desired arrangement of a set of bristle bundles in a brush. The magazine may hold sets of bristle bundles for a plurality of brushes and may be arranged and constructed to clamp and release the set of bristles for each brush independently. For example, the magazine may be arranged and constructed to hold at least four sets of bristle bundles. Each channel may include an opening into the mold cavity portion with a slotted sleeve.
The magazine may further include a detachable trim plate in cooperation with the mold cavity portion. The trim plate includes channels which coincide with the channels through the magazine. A surface of the trim plate may project above the mold face or be flush with the mold face when the plate is in cooperation with the mold cavity portion. When the magazine is seated in an injection molding apparatus, the mold cavity portion of the magazine may cooperate with the mold cavity portion of the apparatus to define a mold cavity having the shape of a portion of the brush. The magazine may further comprise a cut plate mounted on the back side of the magazine with channels coinciding with the channels through the magazine. A portion of the channels may be skewed with respect to one another or lie in intersecting planes.
In another aspect, the invention is a method for processing bristles for a brush. The method comprises holding the bristles in bundles in a magazine, adjusting the relative height of at least a portion of the bristle bundles with respect to one another, trimming non-use ends of at least a portion of the bristle bundles to produce a level plane, heating the non-use ends of the bristle bundles to melt the ends of the bristles, and end-rounding use-ends of the bristle bundles. The step of adjusting may be performed with pins which approach both ends of the bristle bundles. Alternatively, this step of adjusting may comprise providing a plate in cooperation with a side of the magazine such that the plate includes holes in an arrangement corresponding to a configuration of the bristles in the magazine such that each hole ends in a surface corresponding to a desired arrangement of bristle strands or the inverse of the desired arrangements of the bristle strands, and pressing an end of the bristle bundles against the surface in the hole with a pressurized fluid. This step of adjusting may further include adjusting the relative heights of at least a portion of the bristles within the bundles with respect to one another.
After the step of heating and melting the non-use ends of the bristle bundles, the melted portion of the bristle bundles may be flattened or brought into contact with a portion of the magazine, or both. A portion of the bristle bundles may be skewed with respect to one another in the magazine or may lie in intersecting planes. The steps of adjusting and trimming may be repeated, and the step of end-rounding may be performed in several steps. Following the steps of heating and melting the ends of the bristle bundles, a diameter of the melted ends of the bristle bundles may be greater than the diameter of the unmelted portion of the bristle bundles. The step of adjusting may be performed prior or subsequent to the step of end-rounding.
In another aspect, the invention is an apparatus for injection molding a plastic article having at least two components. The apparatus comprises a first and a second injection molding machine each of which comprises at least a first injection unit. The apparatus can be operated in one of two modes. The first mode comprises injection molding a first component of the plastic article at the first injection unit on the first injection molding machine and injection molding a second component of the plastic article at the first injection unit on the second injection molding machine. The second mode comprises injection molding a first component of the plastic article at the first injection unit on the first injection molding machine or the second injection molding machine and injection molding a second component of the plastic article at a second injection unit on the injection molding machine at which the first component was injected. The first component may comprise polypropylene, cellulose propionate acetate, polyethylene terephthalate, or a thermoplastic polymer. The second component may comprise a thermoplastic polymer or a thermoplastic elastomer. The apparatus may comprise first, second, and third injection molding machines. If the apparatus includes a third injection molding machine, the first component may be injection molded in either of the first or second injection molding machines in the first mode.
The apparatus may further include a conveyer system which delivers a holder comprising part of the mold cavity to the injection unit at which the first component is injected and which delivers the holder and the first component of the plastic article to the injection unit at which the second component is injection molded. The apparatus may further include a computer which chooses to which injection unit to send the holder for the first injection molding step and the second injection molding step. At least one of the injection molding machines may comprise first, second, third, and fourth injection units. The first and second injection units may be operated together and the third and fourth injection units may be operated together.
In another aspect, the invention is an apparatus for producing a brush by injection molding. The apparatus includes at least one station at which bristle bundles are fed into channels in a magazine, a station where at the relative heights of the bristle bundles in the magazine are adjusted, a station at which non-use ends of the bristle bundles are trimmed in a level plane, a station at which non-use ends of the bristle bundles are fused, a station at which the use-ends of the bristle bundles are end-rounded, a first injection unit, and a conveyer which transports the magazines to the different stations. At least a portion of the magazine forms part of a mold cavity in the first injection unit. The level plane may be defined by a trim plate in cooperation with the magazine. The apparatus may further comprise a return conveyer to return the trim plate to an unfilled magazine. The bristle bundles may be fed into the magazine from an endless supply, for example, a creel system, or from a pre-cut supply of bristles.
The relative heights of the bristle bundles may be adjusted by pins entering the magazine from a first and a second side. The magazine need not be perpendicular to the pins, and an end surface of a portion of the pins need not be perpendicular to their longitudinal axis. The station at which the relative heights of the bristles are adjusted may include an insert having holes in an arrangement corresponding to the configuration of the bristle bundles in the magazine, wherein the insert is placed in contact with the magazine such that the channels are co-axially aligned with the holes, and a source of pressurized air configured to be in fluidic communication with the channels such that the bristle bundles are interposed between the source of pressurized air and the holes. Each hole ends in a surface corresponding to a desired arrangement of bristle strands or the inverse of the desired arrangement of bristle strands. The relative heights of the individual bristles within the bristle bundles may be adjusted at the station at which the relative heights of the bristle bundles are adjusted. Some of the bristle bundles may be skewed with respect to one another or lie in intersecting planes. The apparatus may comprise at least two stations at which bristle bundle heights are adjusted and two stations where at the bristle bundles are trimmed. If so, then the height adjustment stations and trimming stations alternate such that at least some of the bristle bundles are trimmed before the magazine enters the second height adjustment station.
The apparatus may further comprise a station at which the fused ends of the bristle bundles are flattened or pressed against a portion of the magazine. The apparatus may include a plurality of injection units configured such that the brush is produced from at least two different polymers. The apparatus may comprise a plurality of injection molding machines, each of which may include a plurality of injection units. The injection molding machines may be configured such that the brush is produced from at least two different polymers.
The apparatus may further comprise a packaging system for the completed brush or a station at which the brush can be ornamented or labeled. The apparatus may also include a return conveyer for the used magazine or stations at which the relative heights of the bristle bundles are adjusted prior to or subsequent to the end-rounding station.